Question: Ben is 15 years younger than Ishaan. Ishaan and Ben first met 3 years ago. Six years ago, Ishaan was 4 times older than Ben. How old is Ishaan now?
Explanation: We can use the given information to write down two equations that describe the ages of Ishaan and Ben. Let Ishaan's current age be $i$ and Ben's current age be $b$ The information in the first sentence can be expressed in the following equation: $i = b + 15$ Six years ago, Ishaan was $i - 6$ years old, and Ben was $b - 6$ years old. The information in the second sentence can be expressed in the following equation: $i - 6 = 4(b - 6)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $i$ , it might be easiest to solve our first equation for $b$ and substitute it into our second equation. Solving our first equation for $b$ , we get: $b = i - 15$ . Substituting this into our second equation, we get the equation: $i - 6 = 4($ $(i - 15)$ $ -$ $ 6)$ which combines the information about $i$ from both of our original equations. Simplifying the right side of this equation, we get: $i - 6 = 4i - 84$ Solving for $i$ , we get: $3 i = 78$ $i = 26$.